In semiconductor manufacturing industry, photolithography techniques usually need to be used to transfer circuit patterns onto single-crystal surfaces or into dielectric layers in order to form effective pattern windows or functional patterns. Specifically, photolithography techniques may be implemented using photo-chemical reaction principles and chemical or physical etching methods.
In order to increase integration density of semiconductor devices and form structures with nanometer-scale dimensions, high-resolution photolithography techniques have been widely used. However, resolution of conventional photolithography techniques has reached its theoretical limitations. In order to overcome limitations of the theoretical resolution of conventional photolithography techniques, a variety of double-patterning processes have been developed including, e.g., litho-etch-litho-etch (LELE) and litho-litho-etch (LLE) photolithography techniques. However, with decrease in pattern dimensions on photo masks corresponding to trenches or through holes, photo mask fabrication has become more complex and more difficult. Accordingly, when through holes or trenches are fabricated to form metal plugs or metal interconnects, the through holes or trenches may have to be fabricated at a low density of arrangement. This cannot meet the requirements for high density and small size for semiconductor devices. In addition, in the existing technology, processes are complicated and have high manufacturing cost.
Therefore, it is desirable to increase density of through holes or trenches for forming semiconductor devices.